Null out threadContext->gba when shutting down
Null out threadContext->gba when shutting down

zerofalcon/mgba,libretro/mgba,sergiobenrocha2/mgba,nattthebear/mgba,sergiobenrocha2/mgba,mgba-emu/mgba,mgba-emu/mgba,jeremyherbert/mgba,fr500/mgba,mgba-emu/mgba,askotx/mgba,jeremyherbert/mgba,Anty-Lemon/mgba,nattthebear/mgba,fr500/mgba,iracigt/mgba,libretro/mgba,iracigt/mgba,mgba-emu/mgba,libretro/mgba,Iniquitatis/mgba,askotx/mgba,bentley/mgba,iracigt/mgba,jeremyherbert/mgba,libretro/mgba,Iniquitatis/mgba,AdmiralCurtiss/mgba,Anty-Lemon/mgba,MerryMage/mgba,cassos/mgba,AdmiralCurtiss/mgba,bentley/mgba,Touched/mgba,askotx/mgba,sergiobenrocha2/mgba,matthewbauer/mgba,cassos/mgba,cassos/mgba,Iniquitatis/mgba,zerofalcon/mgba,sergiobenrocha2/mgba,zerofalcon/mgba,jeremyherbert/mgba,MerryMage/mgba,matthewbauer/mgba,Anty-Lemon/mgba,AdmiralCurtiss/mgba,Anty-Lemon/mgba,Touched/mgba,Touched/mgba,libretro/mgba,fr500/mgba,MerryMage/mgba,iracigt/mgba,fr500/mgba,Iniquitatis/mgba,askotx/mgba,sergiobenrocha2/mgba